1. Technical Field
The present invention relates to a thermoplastic elastomer comprising a polyether component (A) as its constituting unit, and to a production method thereof. The present invention also relates to a fiber made from said thermoplastic elastomer possessing excellent water absorption and moisture-releasing property, and to a fabric made from said fiber.
More particularly, the present invention relates to an elastomer sheet possessing excellent moisture permeability and cut-off performance made from a thermoplastic elastomer comprising a polyether component (A) as its constituting unit, and to a production method thereof.
The present invention also relates to a moisture permeable waterproofing fabric possessing excellent moisture permeability and waterproofing property simultaneously, and to clothes, tents, and shoes that are made from said fabric.
The present invention also relates to a molded product, which is employed in the fields of medical treatment, hygiene, or pharmaceuticals. More particularly the present invention relates to a molded product for medical use, for example, containers such as infusion bags or blood transfusion bags, and the like; tubes used for infusion set, blood transfusion system, or catheter; or injection-molding parts such as stoppers thereof.
2. Background Art
In recent years the notion toward preservation of the environment has been raised, and which results in accelerating replacement of existent raw materials with recyclable ones in various industrial fields. With regard to the rubber materials, thermoplastic elastomers (TPE) have been the focus of attention for a long period, and are employed in the field of various industrial products for various applications.
Among them, thermoplastic polyester elastomers (TPEE) are known to possess excellent mechanical strength, heat resistance, abrasion resistance, and bending-fatigue resistance, and have been used in a wide industrial field such as the field of automobiles.
The thermoplastic polyester elastomer (TPEE) is roughly classified into the polyester-polyether type and the polyester—polyester type, the former of which is the present mainstream.
Polyester-polyether elastomers are obtained from the ester-interchange reaction followed by the condensation reaction under vacuum using, for example, dimethyl terephthalate, 1,4-butanediol, and poly-tetramethylene glycol as the starting materials.
In more detail, they are multi-block copolymers made from the hard segment comprising condensation product of 1,4-butanediol and terephthalic acid, and the soft segment comprising condensation product of polytetramethylene glycol and terephthalic acid.
Such thermoplastic polyester elastomers usually have high stiffness compared with ordinary rubber, and are devoid of flexibility. In addition, they exhibit large permanent compression strain under high temperatures and large deformation, thus they are devoid of settling resistance. These defects have long been expected of better modification.
In adding further flexibility to thermoplastic polyester elastomers, it is necessary to reduce the amount of hard segment component that takes charge of physical cross-linking. An existent technique such as disclosed in Japanese Patent Publication for Laid-Open 88632/1990, however, decreased the block property of the hard segment component causing problems such as lowered melting point and inferior mechanical strength at high temperatures.
Concerning the settling resistance, as is disclosed in Japanese Patent Publication for Laid-Open 121699/1977, another technique which improves the settling resistance by raising the polymerization degree. But it had its limitations, and compatibility of settling resistance and flexibility was difficult to obtain.
On the other hand in the field of sanitary products or fabrics, raw materials with excellent moisture permeability are the present focus of attention. As is disclosed in Japanese Patent Publication for Laid-Open 111847/1984, the moisture permeability may be improved by specifying the composition and the amount of soft segment.
Also, as is disclosed in Japanese Patent Publication for Laid-Open 290714/1987, thermoplastic urethane elastomers are known to possess excellent moisture permeability. However, the moisture permeability of these existent materials is still insufficient and a further improvement is desired. Besides, in the case of urethane resins made from para-phenylene-diisocyanate, which is used very frequently, the product discolorates under the radiation of light. This also remains a point to be improved.
There have been many assiduous investigations concerning alternative use of polyester resins instead of polyurethane resins for production of composite sheets. Since polyester resins, however, usually show low solubility in various solvents compared with polyurethane resins, there are the restrictions to the processing method in actual application. In Japanese Patent Publication for Laid-Open 311233/1996, a method of applying a solution of polyester elastomers on a base material with heating, followed by solidifying under cooling and wet-forming the film to obtain a porous film is disclosed.
Fibers made from raw materials that have excellent water absorption and moisture-releasing property are known to exhibit superior sweat absorption as well as excellent treatment of sweat in, and to provide fabrics having dry touch and are smooth.
In the past, polyurethane elastomer fibers have been used as the elastomer fibers. In recent years, however, new polyester elastomer fibers have been the focus of attention, which are made from the hard segment comprising highly crystalline polyester such as polyethylene terephthalate or poly-butylene terephthalate, and the soft segment comprising polyalkylene glycol such as polytetramethylene glycol. However, these materials are still hydrophobic, and accordingly show limited moisture absorption in a fabric form. Thus it was impossible to provide a fabric with dry touch.
As a raw material with excellent water absorption and moisture-releasing property, Japanese Patent Publication for Laid-Open 111847/1984 discloses a ester elastomer having excellent water absorption and moisture-releasing property, which is produced by specifying the composition and amount of the soft segment. Also Japanese Patent Publication for Laid-Open 290714/1987 discloses a novel thermoplastic urethane elastomer. All these products, however, exhibited unsatisfactory moisture absorption and drying property.
The thermoplastic polyester elastomers are also known to be used for films or sheets. (see Japanese Patent Publication for Laid-Open 133032/1982.) Such films or sheets still leave room for improvement about flexibility, and are difficult to provide the products to some fields that really need for the elastic property. Overall in the past, a practically usable film or sheet was unobtainable, which can exhibit sufficient mechanical properties such as strength or flexibility or the like as well as satisfactory heat resistance simultaneously.
The fabrics that possess moisture permeability and water proofing property simultaneously can release steam due to sweat of bodies from the fabrics yet prevent penetration of rain into the fabrics. In order to add such functions, coating or lamination of polyamino acid urethane resins, polyurethane resins, or polytetrafluoroethylene resins on a fabric is well-known.
A fabric coated with ordinary polyurethane resins has shown a defect of steamy feeling in wearing fabrics due to its inferior moisture permeability. In order to solve the problem, proposed is a method of applying a mixture of polyurethane resins and hygroscopic charcoal powders on a fabric. (Japanese Japanese Patent Publication for Laid-Open 13277/1997.) A fabric laminated with micro-porous film of polytetrafluoroethylene shows excellent moisture permeability and waterproofing property. But the micro-pore is easily stuffed up with dusts leading to the inferior moisture permeability. The produced fabrics feel hard, thus are not suited for practical use, especially for fabrics, but the applications are not limited.
Molded products of plastic resins have long been employed in a wide field of medical treatment, hygiene, or pharmaceuticals. They have been used largely as they are light-weight and free from damages compared with metals and glass, can be molded into various shapes such as film or tube, and can be applied to disposable application due to their rather inexpensive costs. Concerning their physical characteristics, durability at sterilization treatment such as steam sterilization under high pressures, radiation sterilization, or sterilization using ethylene oxide is required. The easiness of treating waste is also required. In addition, the transparency of the base material is needed in some uses.
Polyethylene plastic resins have generally excellent impact resistance, flexibility, and transparency, but do not endure high pressure steam sterilization individually at not less than 110° C. owing to their low melting points. For the reason, it becomes necessary to lower the temperature of sterilization and to prolong the sterilization time accordingly. High-density modification of the resin improves the heat resistance, but, on the other hand, sacrifices transparency or flexibility instead.
Polypropylene resins exhibit higher softening points and heat resistance compared with polyethylene resins. But they often lack enough flexibility and impact strength especially at low temperatures, when used alone, for soft bags, films, or tubes due to their rather high modulus of elasticity. Therefore, they are generally employed as blends with other soft resins or elastomer resins, or multi-laminated molded products.
EVA (Ethylene-Vinyl Acetate) copolymers have excellent transparency and flexibility, but show inferior heat resistance. Besides they frequently cause bleed-out of the acetate component by heating or sterilization. In order to obtain heat resistance, it is necessary to add a process of cross-linking using radiation of electron beam.
In order to solve these problems, Japanese Patent Publication for Laid-Open 337164/1993 and Japanese Patent Publication for Laid-Open 317411/1993 disclose medical materials using various cyclic polyolefin resins such as norbornene resins or cross-linked cyclic polyolefin resins. With regard to PVC resins, they generate dioxins, which has a bad influence on the environment at disposal, thus there is a hesitation to use it.